A number of systems and programs are offered on the market for the design of parts or assemblies of parts, such as the one provided by DASSAULT SYSTEMES under the trademark CATIA. These systems and programs, also called computer-aided design (CAD) systems, allow a user to construct and manipulate complex three dimensional (3D) models of objects or assemblies of objects. CAD systems thus provide a representation of modeled objects using edges or lines, in certain cases with faces. Lines or edges may be represented in various manners, e.g., non-uniform rational B-splines (NURBS). These CAD systems manage parts or assemblies of parts as modeled objects, which are mainly specifications of geometry. In particular, CAD files contain specifications, from which geometry is generated. From geometry, a representation is generated. Specifications, geometry and representation may be stored in a single CAD file or multiple ones. CAD systems include graphic tools for representing the modeled objects to the designers; these tools are dedicated to the display of complex objects—the typical size of a file representing an object in a CAD system extending up to the range of a Mega-byte for part, and an assembly may comprise thousands of parts. A CAD system manages models of objects, which are stored in electronic files.
Obviously, modeled objects designed with the help of CAD systems aim at resembling as closely as possible to the final fabricated product, at least for some applications.
For example, in the field of product/part molding, use is made of molds which can be regarded as continuous faces, possibly separated by sharp edges. The real edges—e.g., of the real molds—are however not perfectly sharp edges but rather show slightly rounded or filleted sections. Thus, when such features are neglected in the corresponding theoretical model, the quantity of material needed for molding slightly differs from that expected from the theoretical model. Obviously, such details may be seen as unimportant as long as one focus on the overall agreement between real and modeled objects. However, this may become of importance when considering mass/continuous production, where the differences between theoretical and real quantity of material necessary for production are substantial, for example during one year. As a simple example, let us consider mass production of a cubic molded product, with edge length L. The rounding of the twelve edges of the cube (sometimes called “beveling”) that occurs with real molding amounts to remove a volume of 3 L r2 (4-π), where r is the radius of the osculating circle. Thus, considering for instance r=L/10, the difference between the volume of the perfect cube and that of the final product amounts to about 2.6%. Therefore, one understands that it is needed to predict as faithfully as possible the features of the final “real” product, should it be for improving forecasting. In other words, it is necessary to improve the agreement between theoretical and real models. In this respect and for some specific applications, e.g., manufacturability or esthetic reasons, CAD users sometimes have to replace sharp edges of theoretical molds or products by rounded edges.
To achieve this, the classic modeling approach is to create fillet-like sections (e.g., a radius to apply on concave edges) of round-like sections (radius to apply on all convex edges) of product edges, one by one. As illustrated in FIG. 1, a model product 10 may thus subsequently exhibit a fillet-like section 12 (hereafter referred to as “fillet”) and/or rounded sections 14 (hereafter “rounds”).
FIG. 2 shows typical results of steps of design of rounds 14 and fillets 12 for a model product 10, as a one-by-one process. Creating rounds and/or fillets according to such a process becomes quickly very complicated when the number of element to model increases. The user has to respect a certain order of steps, which may vary according to the modeled object. If not, the rounding or filleting design may fail. The complexity of the modeled object (multiplicity of edges, corner areas, etc.) may be an additional source of failure. In particular, modeling rounds or fillet where edges collide (corners, hard zones, etc.) is a torment. Further, traditional filleting process constrains the model to be made of valid closed geometry between each operation (due to internal constraints in the algorithms used). This constraint often leads manual filleting or rounding to fail. To avoid that, the user has to spend a huge amount of time in order to determine the sequence of creation of the fillets or rounds needed to modify the sharp edges.
Therefore, there is a need for a solution improving the efficiency of product surface fine design and, in particular, improving the rounding and/or filleting process.